A seal is a device for making an impression in wax, clay, paper, or some other medium, including an embossment on paper, and is also the impression thus made. The original purpose was to authenticate a document, a wrapper for one such as a modern envelope, or the cover of a container or package holding valuables or other objects. The sealing process is essentially that of a mould, with the final image represented on the device for making the impression by a mirror-image design, incised in sunken- (or counter-) relief or intaglio.

The seal-making device is also referred to as the seal matrix or die; the imprint it creates as the seal impression (or, more rarely, the sealing). If the impression is made purely as a relief resulting from the greater pressure on the paper where the high parts of the matrix touch, the seal is known as a dry seal; in all other cases a liquid or liquified medium (such as ink or wax) is used, usually in another color than the paper.

For legal purposes, the definition of a seal may be extended to include rubber stamps, or writing specified words ("seal" or "L.S.").

Seal commonly refers to:

Seal may also refer to:

Device is usually a constructed tool, but may refer more specifically to: